The present invention relates to a small-sized one-way clutch having an outer ring of a shell type.
In a small-sized one-way clutch provided with an outer ring of a shell type formed by bending a thin plate, a plurality of cam faces formed at an inner peripheral face of the outer ring are made to be longer than a length of a roller in an axial direction to thereby constitute recess portions for preventing turning of retainers. That is, the retainer provided on the inner side of the outer ring for holding the roller is formed with a projected portion at an outer periphery of one end portion thereof in an axial direction in correspondence with a position of each cam face of the outer ring. By engaging each projected portion with the recess portion extended from each cam face of the outer ring, relative rotation between the outer ring and the retainer is prevented.
Further, there is known a one-way clutch of this kind of a type of forming each cam face at an inner side thereof by expanding a thin plate constituting an outer ring to an outer peripheral side (refer to, for example, JP-B-2-56528). An example thereof is shown by an axially orthogonal sectional view of an essential portion in FIG. 5.
An outer ring 51 made from a thin plate is formed with a portion 51a expanded to an outer side thereof at a constant pitch in a peripheral direction to thereby form a cam face 51b at an inner side portion thereof. Rollers 52 are respectively arranged to an inner side thereof to be brought into contact with each cam face 51b and a shaft 53 is inserted into an inner side thereof. In this example, each roller 52 is urged in a direction of an arrow mark L by a spring 55 integrally formed with a retainer 54 in a state of being contained in a pocket 54a of the retainer 54. Further, in FIG. 5, the spring 55 is shown in a free state and is actually brought into a state of being flexed by being brought into contact with a surface of the roller 52.
The one-way clutch of this kind is used by being fixedly fitted into a hole formed at a central potion of an outer ring fitting member (hereinafter, such a member is referred to as housing member for convenience in the specification) of, for example, a pulley, a gear or the like. Prevention of rotation between the housing member and the outer ring 51 is carried out by constituting a shape of an inner face of the hole of the housing member by a shape by which an outer peripheral face of the outer ring 51 including the expanded portion 51a is fitted thereinto.
Meanwhile, according to the above-described small-sized one-way clutch of the shell type, when comparatively large radial load is operated to the one-way clutch in idly rotating the one-way clutch, for example, when the shaft 53 side is used as an input, a force for carrying to turn the roller 52 by the shaft 53 is increased. When the force exceeds a engaging force (latch strength) between a recess portion of the outer ring 51 extended from the cam face 51b for preventing turning and a projected portion of the retainer 54, as exemplified in FIG. 6, the roller 52 pushes to turn the retainer 54 in the idly rotating direction F and a positional relationship between the outer ring 51 and the retainer 54 in the peripheral direction is shifted. A recess portion of the outer ring 51 for preventing turning is constituted by a sectional shape substantially the same as a sectional shape of the cam face, is comparatively shallow and is of a curved face and therefore, it is difficult to increase the above-described latch strength.
Further, when the above-described positional shift of the retainer 54 relative to the outer ring 51 in the peripheral direction is brought about, in the case in which the shaft 53 is rotated to a locking side thereafter, as shown by FIG. 7, not only the force of urging the roller 52 by the spring 55 is reduced but also the roller 52 interferes with a pillar 54b of retainer 54 disposed in the locking direction and the roller 52 cannot move to a locking position to thereby amount to a problem of bringing about a failure in locking.